Improved seal

ABSTRACT

A seal arrangement includes a plurality of seal elements arranged in series. At least one seal element has a predetermined rated pressure and includes a relief arrangement permitting relief of pressure across the seal element at a predetermined level lower than said rated pressure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a multiple element seal, such as a seal for use in a downhole environment. The seal may include swellable elements.

2. Description of the Relevant Art

Applicant supplies packers, in the form of full joint seal sections, under the E-ZIP trade mark. These packers comprise a number of discrete spaced-apart annular seal elements mounted to a base pipe. A packer is incorporated into a pipe or tubing string and run into a drilled bore, such as are used to access subsurface hydrocarbon-bearing formations. The bore may be lined with casing or may be unlined. The seal elements include swellable elastomer which will swell when exposed to an activating substance, typically water or oil. The seal elements may thus increase in diameter to occupy and seal the annulus between the base pipe and a surrounding bore wall.

The E-ZIP packer thus provides a series of individual seal locations and is thus capable of holding an elevated pressure differential significantly higher than the pressure holding capabilities of packer having only a single seal element.

SUMMARY OF THE INVENTION

According to an embodiment there is provided a seal arrangement including a plurality of seal elements arranged in series, at least one seal element having a predetermined rated pressure and including a relief arrangement permitting relief of pressure across the seal element at a predetermined level lower than said rated pressure without harming the seal's integrity.

According to another embodiment there is provided a seal method that includes providing a series of seal elements and permitting relief of pressure across at least one of said seal elements at a pressure differential below a predetermined rated pressure.

The arrangement allows pressure relief across the at least one seal element before the pressure acting across the element reaches the predetermined rated pressure, which may be the maximum safe or fail pressure of the seal element. Thus, by controlled relief of pressure, the pressure across the seal element may be maintained at a level below the rated pressure, minimizing the risk of seal failure. The pressure bleeding across the seal element may be held by an adjacent seal element.

Two or more seal elements of the seal arrangement may include respective pressure relief arrangements, facilitating equalization of the pressure drop across the individual seal elements of a multiple seal element sealing arrangement. Some or all of the seal elements may include pressure relief arrangements.

Detailed analysis and testing of conventional seal arrangements having multiple seal elements has revealed that the first seal element, looking from the high pressure side, tends to experience the largest pressure drop, with subsequent seal elements experiencing progressively lower pressure drops. When the first seal element experiences a pressure differential above its pressure limit, the seal element may fail suddenly, exposing the second element to a sudden pressure increase. The ability of the second seal element to hold the increase in pressure appears to depend to some extent on the shock absorbing characteristics of the element, and in such circumstances the pressure limit of the element is likely to be lower than if the element had been exposed to a gradual pressure increase. Also, a sudden failure of a seal element may result in damage to the seal element, reducing subsequent sealing ability. In the worst case, failure of the first element may lead to a domino-like failure of subsequent seal elements and irreparable damage to the seal elements.

In embodiments described herein, the likelihood of a sudden failure of a seal element is reduced, and even in the unlikely event of an element failure subsequent seal elements are more likely to be pre-loaded and thus less vulnerable to failure resulting from shock-loading.

The arrangement may be adapted for use in downhole applications, such as within bores drilled to access subsurface hydrocarbon-bearing formations and may be in the form of a packer. However, the arrangement may have equal utility in other applications.

One or more of the seal elements may include a swellable material, such as a swellable elastomer. Such a material may swell when exposed to a suitable activator. The activator may be a substance, for example water or a hydrocarbon, or may be a condition, for example a particular pressure, temperature, or electro-magnetic radiation at a particular wavelength.

The seal arrangement may take any appropriate form. In one embodiment the seal arrangement includes a base pipe providing mounting for a series of annular seal elements, which may be axially spaced. Activation or energizing the seal elements results in the radial extension or expansion of the seal elements to engage and seal with a surrounding bore wall, which bore wall may be formed by installed tubing, such as casing or liner, or by unlined drilled bore.

The relief arrangement may take any appropriate form, and may include one or more valves, which may be one-way valves. The valves may permit a controlled flow or bleed of fluid when exposed to a predetermined pressure differential. The valves may be mounted within a seal element including a swellable material.

Alternatively, the relief arrangement may be provided by selecting an appropriate configuration or material for the seal element. For example, the seal element may include a relatively hard surface-defining portion which will permit low flow rate fluid passage between the seal element and an opposing surface at a pressure differential lower than the normal rated pressure of the element. The provision of a harder material also minimizes erosion to the element by the passage of the bleed fluid.

The relief arrangement may be arranged to operate only in a single direction, or may be arranged to provide for relief in two opposite directions across the seal arrangement. The latter configuration has the advantage that the orientation of the seal arrangement is immaterial to the operation of the arrangement, such that it is not possible to install the seal arrangement the wrong way round. Also, this offers greater flexibility in operation of the arrangement, allowing the seal arrangement to be utilized in applications where the arrangement may experience pressure in different directions.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a view of an a sealing arrangement in accordance with a first embodiment;

FIG. 2 is an enlarged sectional view of area 2 of FIG. 1 in an initial configuration;

FIG. 3 is a sectional view corresponding to FIG. 2, but illustrating the sealing arrangement in an activated configuration in an unlined borehole;

FIG. 4 is a sectional view of a second embodiment in an initial configuration; and

FIG. 5 is a sectional view corresponding to FIG. 4, but illustrating the sealing arrangement in an activated configuration in an unlined borehole.

While the invention may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is first made to FIG. 1 of the drawings, which illustrates a sealing arrangement in accordance with a first embodiment in the form of a packer 10. The general configuration of the packer 10 is similar to that of the packer supplied by the applicant under the E-ZIP trade mark, in that the packer 10 includes a base pipe 12, for incorporation in a pipe or tubing string, and a series of thirteen seal elements 14. Each seal element 14 is of similar construction and includes an annular band of swelling elastomer. In use, the packer 10 is incorporated in a pipe or tubing string and run into a bore to a desired location, with the elements in an initial, smaller diameter configuration (FIG. 2). Exposure to the ambient fluid in the bore results in the seal elements 14 expanding to fill and seal the annulus between the base pipe 12 and the surrounding bore wall 15 (FIG. 3).

Reference is now made in particular to FIGS. 2 and 3 of the drawings, which illustrate two of the seal elements 14 a, 14 b in section. Each element defines two bypass passages 16 a,b, 18 a,b, each passage being provided with an oppositely directed spring-loaded one-way valve 20 a,b, 22 a,b arranged to open at 80% of the seal element rated pressure.

The passages 16 a,b, 18 a,b and valves 20 a,b, 22 a,b are formed of an appropriate rigid material, such as stainless steel, such that they are not adversely affected by the swelling of the elastomer.

On exposure of an activated first seal element 14 a to a pressure differential at or above 80% of the seal element failure pressure, the relief valve 20 a opens, as illustrated in FIG. 3, allowing pressure to bleed through the element 14 a into the annulus 24 between the elements 14 a, 14 b. Similarly, if the pressure differential across the second element 14 b then rises to 80% of the seal element failure pressure, the relief valve 20 b will open, allowing pressure to bleed through the element 14 b. This process may continue along the length of the packer 10, ultimately resulting in an equalization of the pressure differentials across all of the individual elements 14. The provision of the relief valves 20 a,b, 22 a,b also protects the elements 14 against overpressures, minimizing that possibility that any element 14 will be exposed to an overpressure, and damaged or subject to sudden failure—this would only occur in the event of a sudden increase in the pressure differential across an element which could not be accommodated by the flow rate through the relief valves 20 a,b, 22 a,b.

The maximum pressure differential that may be withstood by the illustrated packer 10 without leaking is thirteen times 80% of the maximum pressure capability of each individual seal element 14. This is significantly higher than a similar packer without the pressure relief feature. Also, in the event that the pressure differential rises above this level the packer will likely not fail completely or be subject to damage but will permit a controlled degree of leakage or bleed-through, and return to a sealing configuration when the pressure differential falls below the maximum level.

The elements 14 a,b are provided with valves 20 a,b, 22 a,b oriented in opposite directions such that the packer 10 will operate in either orientation.

In a downhole environment the ambient fluid will tend to carry particulates which could impact on the operation of the valves 20 a,b, 22 a,b. To avoid such difficulties the valves 20 a,b, 22 a,b and passages 16 a,b, 18 a,b may be protected by filters or screens. Alternatively, or in addition, the passages 16 a,b, 18 a,b and valves 20 a,b, 22 a,b may be initially filled with clean fluid such as a high temperature grease. The volume of fluid which moves through the valves to provide pressure relief is relatively small, and thus the clean fluid is unlikely to be displaced from the valves by the ambient fluid, thus protecting the valves from contamination.

Reference is now made to FIGS. 4 and 5 of the drawings, these drawings illustrating part of a packer including an alternative form of seal element 30. Each element 30 includes an inner band of swellable material 32 and an outer band of conventional elastomer 34. The outer band 34 has an external surface featuring sealing lips 36 which are configured to deflect a small amount in response to a pressure differential of 80% or more of the seal element fail pressure. This deflection, as illustrated in exaggerated form in FIG. 5, permits a limited and controlled degree of leakage past the activated element 30 a, as illustrated in FIG. 5, and into the annular chamber 38 between the element 30 a and the next element 30 b.

Those of skill in the art will recognize that the principle of controlled relief of a seal element, and in particular relief of seal elements in a multiple seal element apparatus, is not restricted to use with seal elements including swellable material, and may be utilized in a wide variety of seal forms and arrangements.

In other embodiments a packer or other sealing arrangement may feature a variety of sealing element forms, and the characteristics of individual sealing elements, or individual relief arrangements, may vary within a sealing arrangement.

Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. 

1. A downhole seal arrangement comprising a plurality of seal elements arranged in series, wherein at least one seal element has a predetermined rated pressure and comprises a relief arrangement contained therein for permitting relief of pressure across the seal element at a predetermined level lower than said rated pressure.
 2. The seal arrangement of claim 1, wherein the relief arrangement is adapted to permit relief of pressure across the seal element without affecting the integrity of the seal element.
 3. The seal arrangement of claim 1, wherein the seal arrangement is configured whereby pressure bleeding across the at least one seal element is at least in part held by an adjacent seal element.
 4. The seal arrangement of claim 1, wherein two or more seal elements of the seal arrangement include respective pressure relief arrangements.
 5. The seal arrangement of claim 1, wherein all of the seal elements include pressure relief arrangements.
 6. (canceled)
 7. The seal arrangement of claim 1, wherein at least one of the seal elements includes a swellable material.
 8. The seal arrangement of claim 1, wherein at least one of the seal elements includes a swellable elastomer.
 9. The seal arrangement of claim 1, wherein the seal arrangement comprises a base pipe providing mounting for a series of annular seal elements.
 10. The seal arrangement of claim 8, wherein the seal elements are axially spaced.
 11. The seal arrangement of claim 1, wherein activation of the seal elements results in the radial extension or expansion of the seal elements.
 12. The seal arrangement of claim 1, wherein the relief arrangement includes at least one valve.
 13. The seal arrangement of claim 11, wherein the at least one valve is adapted to permit a controlled flow or bleed of fluid when exposed to a predetermined pressure differential.
 14. The seal arrangement of claim 11, wherein the at least one valve is mounted within a seal element comprising a swellable material.
 15. The seal arrangement of claim 1, wherein the relief arrangement is provided by selecting an appropriate configuration or material for a portion of the seal element.
 16. The seal arrangement of claim 14, wherein at least one seal element includes a relatively hard surface-defining portion adapted to permit low flow rate fluid passage between the seal element and an opposing surface at a pressure differential lower than the normal rated pressure of the element.
 17. The seal arrangement of claim 1, wherein the relief arrangement is adapted to permit relief only in a single direction across the seal arrangement.
 18. The seal arrangement of claim 1, wherein the relief arrangement is adapted to permit relief in two opposite directions across the seal arrangement
 19. A downhole seal method comprising: providing a series of seal elements, wherein at least one seal element comprises a relief arrangement contained therein; locating the seal elements downhole; and permitting relief of pressure across the at least one seal element through the relief arrangement at a pressure differential below a predetermined rated pressure of the at least one seal element.
 20. The method of claim 19, comprising permitting relief of pressure across a plurality of the seal elements at a pressure differential below the rated pressure of the respective seal elements.
 21. The method of claim 20, comprising permitting equalization of pressure differential across multiple individual seal elements. 22-23. (canceled)
 24. The method of claim 18, comprising locating the seal arrangement downhole.
 25. The method of claim 18, comprising providing at least one seal element including a swellable material and exposing the seal element to a suitable activator.
 26. The method of claim 18, wherein relief of pressure across the seal element occurs without affecting the integrity of the seal element.
 27. A downhole seal arrangement comprising: a base pipe; and a plurality of seal elements arranged in series along the base pipe and configured to be activated to radially expand to engage and seal a surrounding bore wall, wherein at least one seal element has a predetermined rated pressure and comprises a relief arrangement contained therein for permitting relief of pressure across the seal element at a predetermined level lower than said rated pressure.
 28. A seal arrangement comprising a plurality of seal elements arranged in series, at least one seal element having a predetermined rated pressure and including a relief arrangement permitting relief of pressure across the seal element at a predetermined level lower than said rated pressure, wherein the relief arrangement includes at least one valve mounted within a seal element comprising a swellable material.
 29. A seal arrangement comprising a plurality of seal elements arranged in series, at least one seal element having a predetermined rated pressure and including a relief arrangement permitting relief of pressure across the seal element at a predetermined level lower than said rated pressure, wherein at least one seal element includes a relatively hard surface-defining portion adapted to permit low flow rate fluid passage between the seal element and an opposing surface at a pressure differential lower than the normal rated pressure of the element. 